How to make the measuring grid larger?
You can change the size of the grid to accommodate your needs, or you can change the scale of the whole scene.
To change the scale of the grid in the 3D view.
For 2.8X Open the overlay controls.

And change the scale and number of subdivisions.
For 2.7X
Press N to reveal the properties shelf.
On the Display section you can change the grid floor number of lines and scale.
The left side of the screen will show info on the scale of the units used.
From the wiki:

Lines defines the number of lines that will make the &quot;floor grid&quot; up. If N is the number defined, there will be a total amount of N/2 lines at each side of X and Y axes. For odd values of N, the amount of lines will be rounded down.
Scale defines the distance between grid lines, either in the &quot;floor grid&quot; and the infinite grid.
Subdivisions defines the amount of lines into which the infinite grid should be subdivided. Level of subdivision depends on zoom, in predefined orthographic views.


To change the scale used for the scene:
Other way to deal with large (or very small) objects is changing the scale on Properties-&gt;Scene-&gt;Units-&gt;Scale


Note that changing the scale for the scene in the Units Section will affect the size of the grid, but changing the size of the grid in the 3d viewport will not change the scene's scale.
Besides the floor grid, Blender has some built in measuring tools that you might find useful.
For 2.8, in Edit mode (Tab), open the Overlays section and you can choose to enable the boxes for Edge Length, Edge Angle, Face Area or Face Angle.

For 2.7X, in Edit mode (Tab), enable the numeric panel (Kbd&gt;N) and look for the Mesh Display section, to enable display of edge and face info of an object.



When dealing with very large or very small objects they might seem to disappear from view due to the clip distance on the viewport. If that happens you might need to change the start and end clip values.
See this question: Why does part of my model disappear when I zoom in on it in the 3D Viewport?